Lymphatic vessels of the dura mater: a new discovery?

Dear Editor, Two recent papers (Aspelund et al. 2015; Louveau et al. 2015) reported the presence in mice of lymphatics in the cerebral dura mater, the most external of the meningeal layers covering the brain. This datum was reported as a novel discovery in the fields of neuroanatomy and neuroimmunology. However, for the sake of clarity, we would like to highlight the following issues: We agree with the authors of the two most recent studies (Aspelund et al. 2015; Louveau et al. 2015) who believe that a better knowledge of dural lymphatics can shed light on the circulation of lymphatic cells from the arachnoid liquid to the venous bloodstream; and, as these cells may be a hallmark of disease, such as neuroinflammatory or neurodegenerative pathologies, the study of these cells may open up new scenarios in the context of CNS disease pathogenesis, early diagnosis, follow up and therapy. We would also like to thank the authors of both papers (Aspelund et al. 2015; Louveau et al. 2015) for having directed their attention to a sometimes forgotten chapter of human anatomy. However, in our opinion, their work has not resulted in a new discovery, nor can they claim that these lymphatics are present in the entire central nervous system, but only in its covering layers. We would like to make these observations known for the benefit of our students and colleagues.